> I tend to agree but, playing devil's advocate, is this true for other roles? Does a movie director need to know how to build sets? How to sew costumes? How to use Blender/Maya/Houdini?

I don't know that much about movie making, but my understanding is that there would be managers and/or leads within each specialty, who are (among other things) managing the interaction between their specialty and the director / producers.

That seems pretty comparable to what's being discussed here.